A vehicle, in particular a passenger vehicle, is generally equipped with a vehicle brake system that has at least one wheel brake for braking a wheel of said vehicle. In this context, the wheel brake is often of hydraulic design and receives a flow of a fluid or brake fluid, which is contained within a fluid line. A hydraulic unit inserted in the fluid line pressurizes the fluid by means of a pump, usually by means of a piston pump for a vehicle brake system having a piston capable of rectilinear movement. During the movement, the piston is guided in a cylinder liner by means of a guide ring. During the movement, the piston performs a guided backward and forward movement within the guide ring.
During the backward and forward movement, the piston enters and exits from a pressure piston, in which the fluid is contained. At the same time, there is air acting on the piston outside said pressure chamber, in particular in a drive chamber for driving the movement of the piston. In this case, the fluid is at least temporarily under high pressure, while the air is under the usual air pressure of the environment.